CPAP treatment is administered when a person is asleep It is therefore crucial that nasal CPAP masks be securely fastened to the wearer's head. Leaks occurring due to mask movement caused by gross body motion during sleep can result in the efficacy of CPAP treatment being defeated. An effective seal of the mask cushion to the patient's face is, in part, a function of the mask design, and is also a function of the correct tension in the harness being maintained. Under-tensioning results in a loose mask and poor seal. Over-tensioning can lead to discomfort for the wearer. All of these problems can lead to patient noncompliance.
A prior art nasal mask and harness arrangement is taught in U.S. Pat. No. 5,243,971 assigned to the University of Sydney. The nasal mask is secured to a wearer's head by a harness comprised of an upper strap and a lower strap, each of which is secured to a frame of the nasal mask. The upper portion of the frame includes a pad that engages the wearer's forehead. The frame farther carries a nasal cushion that, in use of the mask, sealingly engages the wearer's nose and face. The frame also carries a mask body to which is connected a flexible conduit for the delivery of breathable gas to the mask and thereafter to an entrance to the patient's airway.
A problem with this arrangement is that the upper and lower straps are made from an elastic or resilient material which lose elasticity with time and become loose fitting about the wearer's head. Furthermore, movement of the wearer during sleep, may cause sliding movement of the straps to the point where the mask can become loose and leaks occur.
Also, the tightening of either the upper or lower strap tends to pivot the mask thereby altering the tension of the other strap making comfortable and correct adjustment difficult and time consuming.
Other harness arrangements, such as that shown in U.S. Pat. No. 5,542,128 in the name of Lomas, include an upper strap around the head and a lower strap around the neck. This arrangement exacerbates the tensioning problem discussed above as rocking of the head moves the face relative to the neck thereby altering the tension of the straps, especially the neck strap.
Another prior art arrangement is disclosed in published Australian Patent Application No. 32914/95 in the name of Buckley-Mendez.
It is important to distinguish nasal masks for the administration of CPAP treatment from respirators or breathing apparatus that are characterised by full face cover and are intended to simultaneously deliver air to the nose and mouth of a conscious and mobile patient. In contrast, CPAP treatment primarily occurs during sleep when the wearer of a nasal mask is mostly immobile and cannot tolerate the discomfort of respirators or breathing apparatus for want of arousing from the sleep state.
The present invention is directed to overcoming, or at least ameliorating, one or more of the disadvantages of the prior art.